This application proposes to extend our knowledge of the role of endothelial injury in vascular disease to the study of the hyperplastic/ hypertrophic response of small arteries to hypertension. The first objective is to explore the extent of endothelial injury and the time course of repair following transient, angiotensin-induced hypertension. The second objective is to explore the hypothesis that smooth muscle hyperplasia and hypertrophy in acute hypertension are mediated by release of platelet-derived growth factor at sites of endothelial denudation. There has been no work done to define the possible role of the platelet in the response of small vessels to hypertension. Moreover, there are no quantitative data to describe the extent of endothelial cell denudation, the rate of repair of the endothelial cell loss, the deposition of platelets at the sites of injury, or the association of increased smooth muscle replication with sites of injury. The proposed studies will utilize electron microscopy, microdissection, morphometry, vascular casting as well as measures of platelet disappearance and release to provide these data.